Many consumer articles such as prescription medicines are provided in the form of tablets or pills. It is desirable to prolong the shelf life of these articles by protecting them from exposure to air, gas and moisture. Some of these articles are hygroscopic making it necessary to protect them from moisture degradation so that they retain their usefulness over prolonged periods; i.e. shelf life stability, until they are consumed.
In order to accomplish these desirable ends, these tablets and pills are typically contained in what are commonly referred to as blister packages; that is, relatively flat packages having a plurality cavities formed in them from suitable moisture/vapor/gas impervious materials which are sealed to each other. The tablets or pills are carried in the cavities and are protected from moisture/vapor/gas degradation until the protective materials are unsealed to remove the pills or tablets to be consumed.
A typical moisture/vapor/gas impervious blister package currently in commercial use comprises two sheets of protective material, one sheet being a three ply laminate consisting of a flexible plastic film, aluminum foil and a resilient plastic film such as nylon. The aluminum foil ply imparts the desired moisture/vapor/gas barrier protection and is the middle ply of the laminate with the flexible plastic film bonded to one surface of the aluminum foil ply and the resilient plastic film ply bonded to the other surface of the aluminum foil ply. The flexible plastic film, typically a polyvinyl chloride (PVC film, is the innermost ply of the package and serves primarily as a sealant, although it also protects the tablets or pills by preventing them from contacting the aluminum foil ply.
Since the aluminum foil ply used is relatively thin, it can be easily punctured and has a tendancy to tear. Consequently, the resilient plastic film is used to protect the aluminum foil ply and prevent it from being torn or punctured as cavities are cold formed in the laminate. After the cavities are formed, tablets or pills can be placed in them and the other sheet, which is typically a two ply aluminum foil/plastic sheet laminate, is overlaid onto and sealed to the tablet carrying sheet as a cover to complete the blister package.
The aluminum foil ply in the cover sheet is typically somewhat thinner (e.g., about 0.02 millimeters) and therefore not as strong as the aluminum foil ply in the tablet carrying sheet which typically has a thickness of about 0.04 millimeters. This enables the pills or tablets to be removed by manually pushing them through and rupturing the cover sheet.
These types of blister packages are uneconomical to produce due to the high cost of the three ply laminate sheet. In addition, cold forming the cavities in the three ply laminate sheet must be done slowly and carefully to avoid tearing or puncturing the aluminum ply thereby decreasing production line output.